This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[committed] Fix linemap corruption after very wide source lines (PR c++/72803)


PR c++/72803 describes an issue where a fix-it hint is to be emitted at
column 512 of a 511-column source line, leading to an ICE.

The root cause is a bug in linemap_line_start, when transitioning from
lines >= 512 in width to narrow lines.

The wide line in the reproducer has a line map with:
  m_column_and_range_bits = 15, m_range_bits = 5
giving 10 effective bits for representing columns, so that columns <= 1023
can be represented.

When parsing the following line,
  linemap_line_start (..., ..., max_column_hint=0);
is called.  This leads to the "add_map" logic, due to this condition:
      || (max_column_hint <= 80 && effective_column_bits >= 10)
i.e. the new line is sufficiently narrower than the old one to
potentially use a new linemap (so as to conserve values within the
location_t space).

It then attempts to avoid allocating a new line map.  Part of the logic
to determine if we really need a new line map is this condition:
   SOURCE_COLUMN (map, highest) >= (1U << column_bits)
The above condition is incorrect: we need to determine if the highest
column we've handed out will fit within the proposed *effective* column
bits, but "column_bits" here is the column plus the range bits, rather
than just the column bits.

Hence in this case linemap_line_start erroneously decides that we don't
need a new line map, and updates the column bits within the existing
line map, so any location_t values we've already handed out within it
that are offset from the start by
  >= (1<<new_column_and_range_bits)
effectively change meaning, leading to incorrect line&column information
when decoding them, and various "interesting" ways for the linemap
code to fail.

The fix is to use the effective column bits in the above conditional.

Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu;
adds 9 PASS results to g++.sum.

Committed to trunk as r244199.

gcc/ChangeLog:
	PR c++/72803
	* input.c (selftest::test_accessing_ordinary_linemaps): Verify
	that the transition from a max line width >= 1<<10 to narrower
	lines works correctly.

gcc/testsuite/ChangeLog:
	PR c++/72803
	* g++.dg/diagnostic/pr72803.C: New test case.

libcpp/ChangeLog:
	PR c++/72803
	* line-map.c (linemap_line_start): When determining if the highest
	column given out so far will fit into a proposed change to the
	current map, use the effective number of column bits, rather than
	the total number of column + range bits.
---
 gcc/input.c                               | 12 ++++++++++++
 gcc/testsuite/g++.dg/diagnostic/pr72803.C |  9 +++++++++
 libcpp/line-map.c                         |  2 +-
 3 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/diagnostic/pr72803.C

diff --git a/gcc/input.c b/gcc/input.c
index 22cc74c..4df47f2 100644
--- a/gcc/input.c
+++ b/gcc/input.c
@@ -1688,6 +1688,17 @@ test_accessing_ordinary_linemaps (const line_table_case &case_)
   linemap_line_start (line_table, 3, 2000);
   location_t loc_e = linemap_position_for_column (line_table, 700);
 
+  /* Transitioning back to a short line.  */
+  linemap_line_start (line_table, 4, 0);
+  location_t loc_back_to_short = linemap_position_for_column (line_table, 100);
+
+  if (should_have_column_data_p (loc_back_to_short))
+    {
+      /* Verify that we switched to short lines in the linemap.  */
+      line_map_ordinary *map = LINEMAPS_LAST_ORDINARY_MAP (line_table);
+      ASSERT_EQ (7, map->m_column_and_range_bits - map->m_range_bits);
+    }
+
   linemap_add (line_table, LC_LEAVE, false, NULL, 0);
 
   /* Multiple files.  */
@@ -1702,6 +1713,7 @@ test_accessing_ordinary_linemaps (const line_table_case &case_)
   assert_loceq ("foo.c", 2, 1, loc_c);
   assert_loceq ("foo.c", 2, 17, loc_d);
   assert_loceq ("foo.c", 3, 700, loc_e);
+  assert_loceq ("foo.c", 4, 100, loc_back_to_short);
   assert_loceq ("bar.c", 1, 150, loc_f);
 
   ASSERT_FALSE (is_location_from_builtin_token (loc_a));
diff --git a/gcc/testsuite/g++.dg/diagnostic/pr72803.C b/gcc/testsuite/g++.dg/diagnostic/pr72803.C
new file mode 100644
index 0000000..0a9a390
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/pr72803.C
@@ -0,0 +1,9 @@
+/* Long line, with a close brace at column 511, hence with the insertion
+   point for the missing semicolon at column 512.  */
+class test {                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  }
+# 1 "" 1
+// The line directive appears to be necessary to trigger the ICE
+// { dg-error "style of line directive is a GCC extension" "" { target *-*-* } .-2 }
+
+/* Verify that we get the correct line and column for the diagnostic.  */
+// { dg-error "512: expected .;. after class definition" "" { target *-*-* } 3 }
diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index 77beaff..b410c00 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -752,7 +752,7 @@ linemap_line_start (struct line_maps *set, linenum_type to_line,
 	 single line we can sometimes just increase its column_bits instead. */
       if (line_delta < 0
 	  || last_line != ORDINARY_MAP_STARTING_LINE_NUMBER (map)
-	  || SOURCE_COLUMN (map, highest) >= (1U << column_bits)
+	  || SOURCE_COLUMN (map, highest) >= (1U << (column_bits - range_bits))
 	  || range_bits < map->m_range_bits)
 	map = linemap_check_ordinary
 	        (const_cast <line_map *>
-- 
1.8.5.3


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]